The generation of helically toothed flank line crowned cylindrical gears in the continuous generating method results in torsioned flanks. One measure of the torsion is the twist. The object to be attained is to avoid the twist or generate a twist that deviates from the “natural twist.”
To attain an object of the invention, i.e. to avoid the twist, it is known from DE 37 04 607 to machine the gears in the continuous diagonal generating method and in doing so, use a volute tool having a pressure angle of the right- and left flanks that decreases continuously proceeding from a maximum value at one end of the worm towards the other end, with the maximum pressure angle of the right flanks at one end of the worm coinciding with the minimum pressure angle of the left flanks, and vice versa. This tool is very difficult to produce and not very flexible to use.
EP 1 036 624 A2 proposes to use a worm with a modified lead as tool. With this tool, the lead of the flanks changes proceeding from one end of the worm toward the other end of the worm in proportion to the distance from the end of the worm, with the maximum lead of the one flank at one end of the worm coinciding with the minimum lead of the other flank at that worm end, and vice versa. This type of tool is flank line crowned or flank line hollow crowned. The tool is supposed to work in the diagonal method. If the axial distance between tool and work piece is kept constant during the machining of a work piece in the dual-flank machining, a flank line crowning on both flanks of the work piece—convex from the outside (positive) or concave from the outside (negative)—as well as a twist are created.
If only the sign of the diagonal ratio D, i.e. the direction into which the tool is displaced during the shift of the axial carriage in the direction of its axis of rotation, is changed for the machining of an additional work piece, flank line crowning and twist are also created on both work piece flanks. However, relative to the work piece machined previously, the twist has a different amount and the opposite sign.
EP 1 036 624 A2 proposes to generate one part of flank line crowning and twist by changing the center distance during the shift of the axial carriage, and a second part with the tool working in the diagonal method, and to coordinate the crowning of the tool as well as the adjustment data of the machine in such a way that the desired values for flank line crowning and twist are created at the work piece.
EP 1036624 A2 also discloses how the associated twist can be calculated from a flank line crowning generated by changing the center distance during the shifting of the axial carriage. The discussion proceeds on the assumption that the twist generated from a flank line crowning generated by a lead modified tool used in the diagonal method can be calculated in accordance with the invention in the same way as the twist resulting from a flank line crowning that was generated by a change of the spacing between the axes (of tool and work piece) during the machining.
Although the use of a lead modified tool in the diagonal method results in a portion of the twist as stated in the above European patent application, said portion—with the amount of flank line crowning being the same—is not different from a portion of the twist that results from a change of the spacing between the axes during the shifting of the axial carriage. A change of the sign of D does not change this portion of the twist.
However, the use of a lead modified tool also creates an additional, previously unknown portion of the offset. Only this portion can be used to influence the twist of the gearing, if the amount of the flank line crowning is specified. Thus, the method proposed in the European patent application cannot avoid the twist if there is flank line crowning, or even create a twist that specifically varies from the “natural twist.”
The invention is therefore based on the problem of developing the generic method in such a way that flank line crowned modified flanks can be generated in the single flank and/or dual flank process with practically any offset, that geometrically simple tools can be used, and that the tool length required for the machining can largely be randomly selected.